CHICAGO — In the boldest statement yet of its intent to sell clean diesel engines in the U.S., Audi organized a 4200—mile fuel economy test drive across America. The route went the long way from New York to Los Angeles, using a fleet of specially prepared Q7, Q5, A4 and A3 vehicles.

We joined the second leg of the event at the W Hotel in Chicago, where we met up with a Q7 3.0 TDI—our ride for the next four days. Q7 #3 had won it's class on the first leg from New York to Chicago, and was well broken in, with more than 7000 miles on its odometer. Let's see how our hypermiing skills fare against the competition. —Jim McCraw

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The Specs

Each of the 16 vehicles came with Audi navigation, Sirius satellite radio, Michelin low—rolling—resistance tires, a fresh tank of Shell ultra—low—sulphur diesel fuel each day, a Nextel phone for emergencies, a satellite tracking system and a Wi—Fi router connected to a separate cell phone. That enabled crews to go to audimileagemarathon.com to track progress as well as send and receive emails and Twitters from the event officials and other participants while en route.

Other than the special equipment, the Q7 Quattro we drove was a standard US—spec vehicle and had Audi's 3.0—liter turbocharged and intercooled direct—injection diesel engine rated at 221 horsepower and 402 lb.—ft. of torque. Although the Q7 TDI diesel isn't yet on sale here, it will be coming soon, at a starting price between $46,000 and $48,000.

The Drive

The event was sanctioned by IMSA, the same group responsible for the American Le Mans Series where Audi races its R10 diesel sports cars. Every vehicle was refueled and had its gas flap sealed and signed by an IMSA official each day.

Audi told us that the formula for winning would entail maintaining a combination of both a high average speed and a very high fuel mileage figure each day. It was altogether a very sophisticated approach, masterminded by Florian Urbitsch the same man who did the Paris—Beijing diesel rally for Mercedes—Benz in 2006, and who now works for Audi.

Our route would take us south from Chicago to Denver—a total of 1800 miles. While some teams taped over the body seams, put cardboard behind the grille to block the air, folded in the rearview mirrors or put extra air in the tires, the PM crew decided to play it absolutely straight, using no tricks other than drafting close behind semis, which we, of course, do not recommend as a normal practice. We set the Q7's suspension to the dynamic mode, which changes the engine's mapping for best control, and we always used the 6—speed automatic's manual mode tapping into sixth gear as quickly as possible after each traffic stop.

We set the adaptive cruise control system to maintain the shortest distance possible between the Q7 and the vehicle ahead of it in traffic, and dialed the speed to 72.5 mph wherever possible. That speed is the engine's sweet spot in top gear, where the torque curve is at its highest, but engine revs are lowest, between 2200 and 2500 rpm.

As you would expect, the traffic density thinned out after each morning's start, and we drove in shifts of about 150—200 miles, using the information provided by Brunhilde, the all—knowing voice of the Audi satellite navigation system. The tracking system under the rear cargo deck would keep watch of our Q7's position, and would cease calculating speed whenever the Q7 was stopped. We used the driver information system screen between the tachometer and speedometer to keep a constant check on our fuel economy and average speed numbers.

From the great city of Chicago, we visited Beale Street in Memphis, the world capital of blues music, and had ribs at B.B. King's rib joint for dinner. In Little Rock for lunch, we visited the Clinton presidential library complex. In Amarillo, we passed the famous Big Texan Steak Ranch, home of the 72—ounce steak dinner—and actually went to a rodeo. In between, we saw the fall foliage, and the ever—changing terrain of middle and mountain America. Best of all, we drove through nine states, and got no tickets, thanks to our Valentine One radar detector.

The Bottom Line

After four long days, the PM team won the Q7 class fuel economy competition, with an overall average fuel economy of 29.6 mpg and an overall average speed of 61.6 mph over the 1842 miles of the second leg. Not bad for a fully laden 5400—pound, seven passenger crossover. So what's next? Perhaps a fuel economy challenge with an Audi R8 TDI? Sign us up.